Linoleum floor covering

ABSTRACT

The invention relates to an electrically conductive floor covering based on linoleum, comprising a wear layer and a sub-layer, whereby the floor covering has an electrical volume resistivity R 1  according to EN 1081, of a maximum 10 7  Ω. The invention also relates to a method for producing said floor covering.

This application claims priority under 35 U.S.C. §119(b) to GermanApplication Ser. No. 19948406.6, filed on Oct. 6, 1999 and PCTapplication Ser. No. PCT/EP00/09830, filed on Oct. 6, 2000 under 35U.S.C. §363.

This invention concerns an electrically conductive floor covering basedon linoleum which comprises a wear layer and an under layer, with thefloor covering having an electrical contact resistance R₁ in accordancewith EN 1081 of a maximum of 10⁷ Ω, and a method for producing the floorcovering.

The market increasingly is demanding PVC-free, light-colored floorcoverings with a low electrical resistance, in particular with a contactresistance R₁ of a maximum of 10⁷ Ω (contact resistance per EN 1081 orelectrical leakage resistance R_(A) per DIN 51 953). Currently thisdemand is met only by electrically conductive rubber floor coverings.Such PVC-free, electrically conductive floor coverings based on rubberare described, for example, in DE 34 40 572 A1, DE 196 49 708 A1, and DE35 45 760 A1.

Recently, however, there has been a heightened demand for floorcoverings based on renewable raw materials, the classic example of whichis linoleum floor coverings. A conventional linoleum floor covering hasa relatively high electrical resistance of around >10¹⁰ Ω. Thereforesuch a linoleum floor covering cannot be used in rooms, the floorcovering of which must have a certain electrical leakage resistance,such as, for example, in operating rooms of hospitals, laboratories, andcomputer rooms. Known for such applications is the reducing of contactresistance of the linoleum floor covering through the addition ofelectrically conductive fillers such as special carbon blacks. Theaddition of special carbon black, however, has the drawback that the useproperties of the linoleum floor covering is deteriorated as a result ofthe relatively large quantity of carbon black required to achieveadequate electrical conductivity. Second, with the addition of carbonblack to the linoleum mixture, possibilities for coloring arepractically not present. Also in the use of metal powders for improvingthe electrical conductivity, the coloring possibilities aresignificantly restricted and in addition there are altered properties inthe mechanical behavior as well as an increase in the weight and asignificantly reduced thermal insulation of the floor covering.Therefore it has not been possible up to the present to achieve aconductive linoleum floor covering with bright color and contactresistance R₁ of less than 10⁸ Ω.

DE 3416 573 and WO 99/10592 concern electrically conductive floorcoverings based on linoleum which through addition of at least onederivative of imidazol, imidazolin, benzixnidazol, or morpholin or acation-active compound of the same is made electrically conductive or isantistatically equipped. Floor coverings of this kind, however, alwayshave a contact resistance RI of approx. <10⁸ Ω, with this valueadditionally depending on the air humidity. In the case of dry air, eventhese values cannot be achieved.

WO 99/04085 describes a floor covering based on linoleum that iselectrically conductive and on which the linoleum wear layer has anirregular pattern, for example marbling, of variously colored zones. Thevariously colored zones are delineated from each other with sharpcontours and demonstrate varying electrical conductivity. Again thezones of this floor covering that are configured so as to beelectrically conductive contain large quantities of a conductive fillermaterial and are therefore very darkly colored. Although according tothe document, a relatively large range of variation of colorconfiguration appears to be possible, in accordance with example 4, byway of example, a third of the floor covering has a dark coloration.Furthermore, despite a relatively dark coloration, the contactresistances of the floor covering according to the document (6) arealways only >10⁷ Ω. It thus is also not possible with a method of thiskind to produce sufficiently electrically conductive floor coveringsthat essentially have a light color tone throughout.

One objective of the present invention therefore is to provide alinoleum strip suitable as floor covering which has a low contactresistance R₁, in particular a contact resistance R₁ of a maximum of 10⁷Ω which in addition is not as strongly independent [sic] on airhumidity, and at the same time has a bright color ton. An additionaltask of the present invention is to indicate a method with which such alinoleum floor covering can be produced.

These objectives are solved with the objects characterized in theclaims.

In particular a floor covering based on linoleum is provided that iselectrically conductive and that has a wear layer (2) and an under layer(3), with the floor covering having an electrical contact resistance R₁of a maximum of 10⁷ Ω per EN 1081.

For determining the electrical resistance of floor coverings thefollowing values are defined by EN 1081, which replaced DIN 51 953:

1. The contact resistance R₁ per EN 1081, which corresponds to leakageresistance R_(A) per DIN 51 953, is the electrical resistance of a floorcovering measured on a sample between the tripod electrode on thesurface of the floor covering and an electrode on the underside directlyopposite it.

2. In contrast, according to EN 1081, resistance to ground R₂,corresponding to resistance to ground R_(E) per DIN 51 953, is theelectrical resistance of a floor covering measured on an installed floorcovering between a tripod electrode pressed onto the upper surface andground.

Designated in the state of the art as “electrically conductive” floorcoverings are floor coverings which have resistance to ground R₂measured according to EN 1081 of<10⁹ Ω.

According to the invention, the floor covering has a contact resistanceR₁ of a maximum of 10⁷ Ω measured according to EN 1081. Also theresistance to ground R₂ of the floor covering is preferably a maximum of10⁷ measured according to EN 1081.

The figures show the following:

FIG. 1 shows a depiction of a schematic cross section through a floorcovering (1) according to a preferred embodiment of the presentinvention along line A—A of FIG. 2. Arranged on a backing (4) are a wearlayer (2) and an under layer (3). Particles (6) can be dispersed in thewear layer which comprise a conductive filler material. Arranged on theside of backing (4) facing away from lower layer (3) in this embodimentis a conductivity web (5).

FIG. 2 shows a schematic view of the underside of a floor covering (1)according to an embodiment of the present invention. Arranged on theside of backing (4) facing away from the lower layer is a conductivityweb (5). During the installation of the floor covering, this web (5)can, for example, be connected to a copper strip tab (7) by means ofwhich the floor covering is grounded through connecting to ground.

The floor covering according to the invention has a lower layer based onlinoleum and a wear layer or top layer based on linoleum. The floorcovering preferably has an overall thickness of around 2 mm to around 6mm, in particular around 2 mm to 4 mm.

According to the invention, the electrical conductivity of the lowerlayer preferably is achieved through mixing at least one electricallyconductive filler material into the linoleum raw mixture. Carbon blackand metal powder are preferred as electrically conductive fillermaterials, with it being possible to use a filler material alone or incombination. In the case of use of carbon black as conductive material,depending on carbon black type, the concentration is preferably about 1%to 20% by weight, more especially preferred about 3% to 15% by weight,in relation to the weight of the conductive mixed mass. By way ofexample, Ketjenblack® EC-300J (Akzo Nobel), Printex® XE 2 (Degussa AG)or one or several other commercially available carbon blacks can be usedas carbon black. In the case of use of metal powder as conductivematerial, the concentration is about 1.5% to 40% by weight, in relationto the weight of the conductive mixed mass. The quantity used is gearedto the density and particle size of the metal powder. By way of example,aluminum, bronze, and VA powder can be used. Any arbitrary mixture ofcarbon black and one or more metal powders as well as a single metalpowder or a mixture of several metal powders can be used. The quantityrelationships in mixtures of carbon black and metal powder are to beselected such that contact resistance R₁ of the lower layer, which inthe floor covering is in contact with the wear layer, is preferably ≦10⁷Ω (EN 1081), still more preferred ≦10⁵ Ω (EN 1081).

The lower layer can contain other chemical additives which furtherimprove the conductivity of the linoleum. By way of example, chemicaladditives of this kind as well as examples of use quantities aredescribed below in association with composition and can be usedanalogously in the lower layer.

In addition to the aforementioned additives, the lower layer hasconventional composition. In particular conventional additives such asprocessing enhancers, antioxidants, UV stabilizers, lubricants, and thelike can be contained in the mixed mass which can be selected dependingon the binder.

The lower layer preferably has a thickness of 0.6 mm to 1.4 mm.

The wear layer or upper layer of the floor covering according to theinvention is the visible surface in the installed floor covering.According to the invention it can have a higher contact resistance R₁than the lower layer and preferably contains only slight quantities ofconductive filler material. A degree of conductivity of the wear layercan be achieved through essentially colorless chemical additives in thelinoleum base mass for the wear layer. Preferably morpholin and/or atleast one derivate of imidazol, imidazolin, or benzimidazol or a mixturethereof are used as chemical additive. Preferably the chemical additiveis worked into the linoleum raw mass in a quantity of 0.5% to 15% byweight, more preferably in a quantity of 4% to 10% by weight in relationto the total weight of the linoleum mass of the wear layer. In the caseof the use of chemical additives of this kind, in a preferred embodimentof the invention diatomite, which is also often designated siliceousearth, can be used as a sorbent. Preferably 3% to 5% by weight diatomitein relation to the weight of the linoleum mixed mass is used.

According to the invention, the wear layer can have a bright color andhave a plain color or a multicolor pattern. In the wear layer,preferably in place of the decorative color which is providedproportionately in the lowest quantity, an electrically conductivefiller such as carbon black and/or metal powder and/or conductive fibersor a mixture thereof are added.

Conductive fibers in the meaning of the invention are in particulargraphitized synthetic fibers or synthetic fibers which are jacketed withepoxy-graphitized material. Conductive fibers of this kind can beproduced through addition of graphite into the synthetic itself orthrough sheathing of small synthetic particles with graphite, and inmost cases have a gray coloration. As a result of their small dimensionsand low additive quantities, however, they appear almost colorless tothe human eye.

In the wear layer, there is preferably 0.1% to 5% by weight, especiallypreferred 0.1% to 2% by weight carbon black and/or 0.1% to 8% by weight,especially 0.1% to 3% by weight metal powder. Through additions of thiskind in small quantities, the conductivity of the linoleum wear layercan be improved to below 10⁷ Ω. Furthermore, as a result of this smallproportion of electrically conductive filler in the wear layer and withthe addition of the above mentioned chemical additives, the contactresistance R1 surprisingly is no longer so strongly dependent on the airhumidity.

In addition, the upper layer comprises the usual components for linoleumfloor coverings such as binding agents (so-called bedford cement or Bcement from a partially oxidized linseed oil and at least one resin astackifier), at least one filler, and if desired at least one colorant.Ordinarily softwood sawdust and/or cork dust (in the case ofsimultaneous presence of sawdust and cork dust, typically in a weightratio of 90:10) and/or chalk, kaolin (China clay), and heavy spar areused as filler. The mixed mass ordinarily contains at least one coloringagent such as a pigment (for example titanium dioxide) and/or otherconventional coloring agents based on inorganic and organic colorants.As coloring agents, any natural or synthetic colorants as well asinorganic or organic pigments, alone or in any combination may be used.A typical linoleum composition contains, in relation to the weight ofthe wear layer, approx. 40% by weight binders approx. 40% by weightorganic fillers, approx. 15% by weight inorganic (mineral) fillers, andapprox. 5% by weight coloring agents. Furthermore the usual additivessuch as processing enhancers, antioxidants, UV stabilizers, lubricants,and the like may be contained in the mixed mass which can be selecteddepending on the binder.

The wear layer preferably has a thickness of 1.4 mm to 3.6 mm,especially preferred 1.4mm to 2 mm.

Surprisingly it was determined that the contact resistance of thecomposite of wear layer and under layer is improved as a result of theconductive under layer compared with the contact resistance of the wearlayer. Without wishing to establish a mechanism, it is assumed for thisembodiment that the small spreading of a conductive material can serveto a degree as bridges or electrical lines between the surface of thefloor covering and the conductive lower layer. As is shown in FIG. 1,according to this embodiment form at least some of the spreading of aconductive material (6) or agglomerates of the same extend through thetotal thickness of wear layer (2) and establish a connection between thesurface of the floor covering and the conductive lower layer (3).

As a further advantage of the present invention, the wear layercontaining only very low quantities of electrically conductive filler toan extent can lie “protectively” or “compensatingly” above the lowerlayer. Since the lower layer can contain relatively large quantities ofan electrically conductive filler, its mechanical properties are oftendeteriorated. These deteriorated properties, however, do not come toplay in the total composite of the floor covering according to theinvention since the wear layer with good mechanical properties liesabove the lower level. By way of example, a somewhat brittle lower levelcan be protected through an elastic wear layer.

Furthermore the linoleum floor covering according to the inventionpreferably comprises a backing. As backing material, a material on thebasis of natural and/or synthetic woven or knitted fabric as well astextile materials can be used. Examples are jute fabric, mixed fabric ofnatural fibers such as cotton and viscose staple fiber, fiberglassfabric, fiberglass fabric coated with bonding agent, mixed fabric ofsynthetic fibers, fabric of core/jacket fibers, for example with a coreof polyester and a jacket of polyarnide. A coating of the fiberglassconsisting of styrene-butadiene latex can be used as bonding agents forfiberglass fabric.

According to one embodiment of the present invention, a back coating canbe applied to the side of the backing away from the lower layer which iselectrically conductive and more preferably is not applied in the formof a continuous coating but rather in the form of a web or strip,preferably of a width of 50 mm to 100 mm and a thickness of 50 mm to 200mm. This preferably web-shaped back coating extends continuously overthe entire length of the floor covering strip. It is in electricalcontact with the lower layer and during installation of the floorcovering can be contacted by way of example with a copper strip tabwhich is connected to ground potential so that the floor covering can begrounded. While in the state of the art, electrically conductive specialadhesives must be used in laying conductive floor coverings in order toestablish contact with ground potential, according to this embodiment ofthe present invention, it is possible to only connect one copper striptab bonded to the web-like back coating to ground potential and to usean ordinary adhesive for laying the floor covering.

Advantageously a web-like back coating is also applied as the back sideof the floor covering is supplied with a stamped imprint through aprinting process. For this purpose aqueous carbon black dispersions andpolymer dispersions, for example a latex, can be used which contain upto 8% by weight, preferably 4% to 6% by weight of an electricallyconductive filler, preferably carbon black. In particular thispreferably web-like back coating comprises a polymer material whichcomprises an electrically conductive filler incorporated therein asdescribed above. An electrically conductive filler incorporated within apolymer material has the advantage that the back coating does not ruboff.

The present invention also concerns a method for producing the floorcovering based on linoleum according to the invention.

For producing the floor covering according to the invention, theconventional methods for producing multiple layer floor coverings can beused.

As a first step, the method according to the invention comprises theapplication of the linoleum mass of the lower layer to a backing. Forthis purpose, all of the components for the linoleum mass as describedabove are mixed in a suitable mixing apparatus, for example a kneader,roll mill, or extruder, into as homogenous as possible base mass (mixedmass). The mixed mass obtained in this manner is added to a roll mill(for example a calendar) and is pressed under pressure and a temperatureof ordinarily 10° to 150° C. (depending on the recipe and processtechnology) onto a backing material. During the pressing of the mixedmass onto the backing material, the roll mill is adjusted (for examplethe distance between the cylinders of a calendar) such that theresulting floor covering strip obtains the desired layer thickness. Inthe linoleum floor coverings according to the invention, the thicknessof the lower layer as described above is 0.6 mm to 1.4 mm.

Next, the linoleum sheet for the wear layer is produced which preferablyis colored and/or patterned.

In the simplest case, particles of a suitable size of an electricallyconductive filler can be spread into a uni-colored or multicoloredlinoleum mass for the wear layer, if desired together with particles ofcolored filler and the linoleum mass can be calendared into a linoleumsheet.

According to one embodiment, colored chips of a linoleum mass, whichpreferably contains electrically conductive filler, can be spread onlinoleum sheets produced in this way and pressed into them.

Furthermore, according to one embodiment, a colored and patternedlinoleum mass can be produced. For this purpose, mixed masses or basemasses of different color are initially produced separately, rolled intosheets, and granulated. Afterwards, different colored granulates aremixed together and then fed to the roll mill (for example a calendar)and formed as a sheet. In special cases, the mixture of differentcolored granulates prior to application to the backing material is drawninto striped sheets, laid rotated 90° to each other and then calendaredwith friction, resulting in pattern forms known as such and suggestiveof natural marble.

According to a further embodiment, sharp-contoured patterns can beachieved in that different rolled sheets are laid one over the other(doubled) and are brought into close contact and only afterwards arecrumbled together. In so doing, particles are created which consist oftwo different parts which are adhering to each other. One partpreferably consists of non-conductive mixed mass and the other partpreferably consists of conductive mixed mass. The multiple layercomposite of the rolled sheet for example can be granulated, cut,broken, or ground in order to produce the particles. Preferably thecomposite is processed into granulate. If these particles or thegranulate of parts of differing mixed mass are now brought to a rollmill such as a calendar and are applied by rolling onto a backing, anirregular pattern is obtained in which the variously colored zoneshanging together and also zones of conductive and non-conductivematerial are delineated with sharp contours from each other and thecolored zones are retained practically pure. These colored zones arebordered by the mixed mass which contain the conductive filler materialand therefore is dark to black colored.

In addition to the above methods for producing a patterned linoleumsheet, all other conceivable methods can be used.

A rolled sheet of wear layer of this kind is then pressed with the lowerlayer into a two-layered linoleum floor covering.

Afterwards the two-layered linoleum floor covering is subjected to thecuring treatment usual for linoleum floor coverings.

According to one embodiment of the method according to the invention, atleast one, preferably web-like, back strip is applied to the back sideof the floor covering. This imprint is preferably applied through apressing process to the back side of the floor covering.

EXAMPLE

A two-layer floor covering according to the invention was produced inthat a lower layer and a wear layer were calendared onto a jute backingand the resulting composite was then cured. The compositions of thelower layer and the wear layer were selected as described in Table 1below.

Leakage resistance R_(A) of the lower layer and leakage resistance R_(A)of the upper layer are also specified in Table 1.

TABLE 1 Lower Layer Upper Layer Components Content (% by weight) Content(% by weight) Cement 38.0 34.0 Sawdust 37.2 32.2 Carbon black,conductive 4.0 0.5 Titanium dioxide — 7.9 Quatenary ammonium 6.7 6.7salt Diatomite 2.4 4.0 Aluminum hydroxide 11.7 13.05 Pigments — 0.85Zinc oxide — 0.8 Leakage resistance 6 × 10³ to 10 × 10³ 2 × 10⁶ to 10 ×10⁶ R_(A) [Ohm]* Note: *Leakage resistance R_(A) was measured based onDIN 51 953, whereby in contrast to DIN 51 953, the upper and lowerlayers were not conditioned in accordance with the standard.

The composite of lower layer and wear layer had a contact resistance R₁per EN 1081 of 1.9×10⁶ to 3.8×10⁶ Ω.

What is claimed is:
 1. An electrically conductive floor covering basedon linoleum, comprising: a wear layer wherein the wear layer comprises0.1% to 5% by weight carbon black or 0.1% to 8% by weight metal powderin relation to the total weight of the wear layer or a combinationthereof; a lower layer, wherein the lower layer contains at least oneelectrically conductive filler material, wherein the electricallyconductive filler material includes 1% to 20% by weight carbon black or1.5% to 40% metal powder in relation to the conductive mixed mass or acombination thereof; a backing layer; and a conductive web strip appliedto a side of the backing away from the lower layer, wherein theconductive web is in electrical contact with the lower layer, andwherein the floor covering has a contact resistance R₁ per EN 1081(April 1998) of a maximum of 10⁷ Ω.
 2. The floor covering according toclaim 1, wherein the lower layer has a thickness of 0.6 mm to 1.4 mm. 3.The floor covering according to claim 1, wherein the wear layercomprises a chemical additive for increasing conductivity.
 4. The floorcovering according to claim 3, wherein the chemical additive is selectedfrom derivatives of imidazol, imidazolin, benzimidazol, morpholin andmixtures thereof.
 5. The floor covering according to claim 1, whereinthe wear layer has a bright color.
 6. The floor covering according toclaim 1, wherein the wear layer has a multicolor pattern.
 7. The floorcovering according to claim 1, wherein the wear layer has a thickness of1.4 mm to 3.6 mm.
 8. The floor covering according to claim 1, whereinthe conductive web strip comprises an electrically conductive fillermaterial.
 9. A method for producing a floor covering based on linoleumaccording to claim 1 comprising applying the lower layer onto thebacking; and forming the wear layer on the lower layer, furthercomprising applying a conductive web strip to a side of the backing awayfrom the lower layer, wherein the conductive web is in electricalcontact with the lower layer.
 10. The method according to claim 9,wherein the back coating is applied through a press process.